Congenital self-healing reticulohistiocytosis has been described as a benign form of Langerhans cell histiocytosis (LCH) that appears during the first 2-3 months of life and then resolves over a period of several months. However, more aggressive forms of LCH have been reported during the neonatal period and may initially be clinically indistinguishable from congenital self-healing reticulohistiocytosis. Continued surveillance and monitoring of patients presumed to have congenital self-healing reticulohistiocytosis is paramount.
LCH, once described as histiocytosis X, is a clonal proliferative disorder of Langerhans cells that stain immunohistochemically with S-100 and CD-1a and demonstrate cytoplasmic Birbeck granules under electron microscopy.  Four variants of this disorder have been described: Letterer-Siwe disease, Hand-Schüller-Christian disease, eosinophilic granuloma, and congenital self-healing reticulohistiocytosis, also termed Hashimoto-Pritzker disease. 
Letterer-Siwe disease is an acute, sometimes fulminant, multisystem disorder that commonly develops during early infancy. Skin findings often demonstrate multiple scaly papules in a seborrheic distribution. Lesions occur in crops and may be crusted or hemorrhagic. Systemic involvement may include the pulmonary system, the liver, the spleen, bone, bone marrow, the hypothalamus, the gastrointestinal tract, and lymph nodes. 
Hand-Schüller-Christian disease is a chronic, progressive, multifocal variant that usually affects adults. This variant has 4 characteristic findings: exophthalmos, diabetes insipidus, bone lesions, and mucocutaneous lesions. Skin lesions often have a xanthomatous appearance. 
Eosinophilic granuloma is a more chronic, localized disorder that most often involves bone. The cranium, ribs, vertebrae, pelvis, scapulae, and long bones may be involved.  Related articles include Eosinophilic Granuloma (Histiocytosis X), Eosinophilic Granuloma, Skeletal, and Eosinophilic Granuloma, Thoracic.
Congenital self-healing reticulohistiocytosis was first reported in 1973 by Hashimoto and Pritzker as a benign, self-limited variant of LCH with only skin involvement.  This variant usually manifests at birth or during the neonatal period as reddish-brown papules or papulovesicular lesions. Lesions resolve within 3 months. Systemic involvement does not develop.
Because skin manifestations of the more aggressive, systemic forms of LCH may initially be lesions that mimic congenital self-healing reticulohistiocytosis, a thorough evaluation for systemic abnormalities must be undertaken. A recent case report highlights the necessity for close follow-up. A 2-month-old Japanese boy was diagnosed with "skin only Langerhans cell histiocytosis" after developing typical skin lesions positive for CD1a with a negative systemic workup. Complete regression of skin lesions occurred by age 9 months. By age 11 months, the patient developed fever, cough, and a left supraclavicular swelling. Workup revealed a mass in the thymus composed of CD1a-positive histiocytes and the patient underwent multiagent chemotherapy.  A review of several similar cases was published in 2012.  One author described two infants who presented with similar clinical manifestations, with one infant having skin lesions involute and remained free of internal involvement but the other infant developed extensive internal involvement. 
Congenital self-healing reticulohistiocytosis is truly a diagnosis of exclusion, and long-term follow-up monitoring for possible relapse or progression of the disease is required.
Langerhans cells arise from bone marrow precursors to populate the epidermis and act as antigen-presenting cells; they play a key role in immune surveillance and contact sensitivity. By the seventh week of gestation, Langerhans cells are found in the epidermis and are found to start expressing CD1a protein by 60 days of gestation.  The clonal, proliferative nature of LCH has long been debated as to whether it represents a reactive or neoplastic process.  A virally induced proliferation of Langerhans cells was disproved by extensive polymerase chain reaction screening for 9 different viruses. 
Elevated levels of cytokines such as tumor necrosis factor-alpha; interferon gamma; granulocyte-monocyte colony-stimulating factor; and interleukins 1, 2, 4, and 10 have been demonstrated in the tissue of LCH lesions. [12, 13] The actual role of these cytokines in the pathogenesis of the disease remains obscure.
Owing to the high rate of spontaneous resolution and lack of clinical recognition, the true incidence of congenital self-healing reticulohistiocytosis may be underreported.  The reported prevalence of LCH in children is 5 cases per million population,  and the incidence rate of congenital self-healing reticulohistiocytosis is much lower.
An annual prevalence of 4-5.4 cases per million population is reported for all forms of LCH, and, since Hashimoto and Pritzker first described congenital self-healing reticulohistiocytosis in 1973, more than 100 cases have been reported.
The prevalence of LCH seems to be higher among whites than persons of other races.
The sex distribution is equal.
The cutaneous lesions of congenital self-healing reticulohistiocytosis typically manifest at birth or during the first 2 months of life. One case report documents the presentation of an 8-year-old girl in Japan who had multiple asymptomatic, reddish-brown papules over her face and upper limbs.  Skin lesions normally resolve over a 3- to 4-month period.
New papules that develop after age 2 months are not typical of congenital self-healing reticulohistiocytosis and should be investigated as possibly being a more aggressive form of LCH. Aggressive forms of LCH may manifest during the neonatal period.
Overall, the prognosis is good, with complete resolution of lesions within 3-4 months of their onset. Some lesions heal with residual hypopigmented, hyperpigmented, or atrophic scars. 
Congenital self-healing reticulohistiocytosis has been regarded as the benign end of the spectrum of LCH. By definition, congenital self-healing reticulohistiocytosis is a self-limited disorder and clinical features should completely resolve over a period of months. The few reports of relapses or the development of systemic LCH after a diagnosis of congenital self-healing reticulohistiocytosis actually represent systemic disease that initially manifested in a manner similar to congenital self-healing reticulohistiocytosis.